Rigid five-coordinate diorganotin derivatives of oxalic acid diamides, studied by 119Sn-NMR and X-ray structural analysis

Bis(2-hydroxy-3,5-di-tert-butyl-phenylanilido) oxalic acid reacts with diorganotin dichlorides, R2SnCl2, in the presence of triethylamine to give the polycyclic bis(diorganotin) derivatives 1, in which the surroundings of each tin atom correspond to a distorted trigonal bipyramid with one nitrogen and two carbon atoms in the equatorial and two oxygen atoms in the axial positions. The solid state structure was established for 1a (R=Me) by X-ray analysis, and the agreement between the 119Sn chemical shift in the solid state and in solution suggests that this structure is retained in solution. It was possible for the first time to determine isotope-induced chemical shifts 1Δ12/13C(119Sn) for five-coordinate tin nuclei at natural abundance of 13C. A positive sign of 1Δ12/13C(119Sn) was found for R=Me (1a), Bu (1b) and Ph (1c).